The present invention relates generally to hydraulic valves and, more particularly, to balanced four-way valves for controlling hydraulic devices.
Hydraulic circuits are known to include valve members which control the application of fluid pressure from a pressure supply line to a plurality of control lines for actuating a hydraulic implement, tool, or device. For example, in lathes and other machine tools, such valve members control the pressure flow between directional control lines for adjusting work supports. In particular, a four-way valve may be mounted between a pressure supply or input line, a pressure return or output line, and left and right pressure control lines. These control lines determine the position of a work support along a typically linear path. The valve member is positionable between left, right and neutral locations. In the left location, the valve member permits pressure flow between the input line and the left control line and pressure flow between the right control line and the output line. In the right location, the valve member permits pressure flow between the input line and the right control line and pressure flow between the left control line and the output line. In the neutral location, the valve member shuts off flow from the input line entirely. Ideally, in the neutral location the valve member would also shut off flow to and from the control lines and output line, thus maintaining the work support at its last adjusted position.
The valve members in such hydraulic circuits have often been spool valves requiring linear motion to actuate between various positions. A significant amount of space along the linear direction of valve motion has typically been required to provide the requisite number of interconnections between pressure lines. Further, such valves have required considerable machining to produce, especially where the level or amount of pressure flow is also to be controlled by the valve member.
Rotary spool or servo valves are available which reduce or eliminate entirely the necessity for linear motion. However, rotary valves typically require a large angle of rotation to switch between all requisite pressure line connections and/or considerable machining of the valve chamber and the valve member itself. Large angles of rotation are particularly undesirable where the valve member is controlled by direct connection to a precision stepping motor, as in a CNC lathe. Excessive machining is undesirable since it increases production costs and assembly time. Some relatively inexpensive rotary servo valve arrangements are known, but these are often merely bi-stable and will not serve to control the amount of pressure flow as well as its direction. Further, a major concern with respect to rotary valves is that pressure imbalances with respect to one or more of the connection lines may cause the valve member to jam against its seat or the valve chamber.
Such pressure imbalances may arise from a variety of sources. With respect to the input line, the supply pressure is often greater than the return pressure or the pressure in the control lines, especially if the valve member has been in its neutral location and there is some leakage from the control lines. This high supply pressure is exposed to a portion of the valve member at the connection between the pressure lines and, thus, forces it against a portion of the valve seat or the valve chamber opposite that exposed portion. It has been suggested to split the passageway through the valve housing from the supply pressure line and provide supply pressure ports on opposing sides of the valve member so as to balance these high supply pressure forces. However, this arrangement significantly increases production costs and complicates the pressure line connection orientation required for the valve member.
Even if the valve member is balanced against supply pressure from the input line, pressure imbalances from either or both of the control pressure lines may detrimentally affect the valve member. The fluid pressure from these lines also acts on an exposed portion of the valve member at the pressure lines connection to force the valve member off center and against the valve seat or valve chamber. High pressures in the control lines can be transitory or sustained and may result where the control lines have been previously charged by the input line with little or no leakage since then or where the control lines are continuously subject to a charge from, for example, connection to a pressure accumulator. To some extent, the effect of control line pressure on the valve member can be balanced by positioning the left and right control pressure line ports to the valve member on opposing surfaces of the valve member. However, the pressure in each control pressure line is not always equal, nor does it always remain constant.
Further, the output line can also exert undesirable pressure on the valve member. High pressures in the return line can result where the hydraulic circuit includes other independently operable devices having a common return line with the valve member. As these other devices are employed, the return line can, at least momentarily, be exposed to output pressures which exceed even the input line pressure and the control line pressures. These high pressures are also exposed to a portion of the valve member and can, thus, force the valve member off center.
Forcing the valve member off center causes increased wear on the valve seat and decreases its useful lifetime. Further, when the valve member is jammed off center, increased torque is required to actuate the valve. This presents a problem particularly where it is desirable to employ a precision stepping motor to control valve position. Higher torque motors are more expensive, and variations in the required torque (as where pressure imbalances vary) can introduce significant errors in precision control of the valve.
Pressure imbalances can occur at any time and at any valve position in the hydraulic circuit. Prior valve systems have often focussed on pressure imbalances occurring when the valve member is in the neutral location and where excess pressure is caused by input line pressure. However, as discussed above, any of the other pressure lines can also cause significant imbalances even at the neutral valve location. Further, pressure imbalances can also occur when the valve member is in the left or right open locations as well as at various stages of these locations (corresponding to control of the amount of fluid flow in each direction). To the extent that there is leakage past the valve seals to the axial ends of the valve member, there can also be pressure imbalances which exert an axial force on the valve member.
Balanced rotary valves have generally been known and, in some applications, have been reasonably successful. These balanced valves typically permit selective interconnection between two or three pressure lines and compensate for inlet line pressure exerted on the valve member. Again, however, pressure imbalances can result from high pressure levels in any of the pressure lines, not just the inlet line. Further, valve constructions which are suitable in specialized two and three-way valve members are often not readily applicable or commercially feasible for mass produced four-way valves. This is especially the case where the pressure line connections are not coplanar within the valve member, but are instead axially displaced (requiring longer valve member dimensions) along the valve. Such arrangements inhibit compact valve design and increase production and assembly costs.
Various four-way balanced valves have been suggested, but these also typically have complicated constructions. For example, pressure line connections are often made through torturous flow paths within the valve member, some of which involve fluid flow constrictions. Also, the valve member may not be capable of isolating the pressures within each of the pressure lines when in the neutral location. This permits undesirable equalization of fluid pressure within the control lines and/or drainage of control line pressure through the return line.
Typically, these valves include cuts or recesses in the valve member, even at the ports to the pressure lines, which increase valve exposure to high pressures with the attendant deterioration of valve sealing integrity. On occasion, balancing has been accomplished merely by draining the excess pressure to the return line or opposing pressure lines, although this results in decreased circuit efficiency.
Prior balanced valves have typically been tapered spool valves. However, these arrangements are more difficult to manufacture and have also required axial balancing since tapered spools tend to be self-locking at one end. Additional mechanical devices, such as springs, have been employed to maintain free valve movement in such tapered valves.
It is therefore an object of the present invention to provide an improved balanced valve for use in hydraulic circuits.
Another object is the provision of a four-way valve which is balanced at any valve location and with respect to pressure from any connecting line.
A further object is to provide a balanced valve which is compact, requires minimal machining, and is commercially feasible to mass produce.
Yet another object is the provision of a balanced rotary valve requiring minimal actuation torque and a small angle of rotation to move between each pressure line connection position.
Still another object is to provide a balanced four-way valve maintaining pressure line isolation at the neutral valve location and minimizing valve member exposure to fluid pressures.
Yet still another object is the provision of an inexpensive four-way valve having hydraulic balancing of the radial valve location, at both open and closed pressure line connection positions, as well as of the axial valve location.
These and other objects of the present invention are attained in the provision of a four-way valve, for selectively interconnecting pressure supply and return lines with control pressure lines of a hydraulic device, having means for independently balancing the valve against pressures exerted on the valve by any one or more of the pressure lines and at any operating position of the valve. These pressures exerted on the valve would otherwise wise restrict or prevent actuation of that valve. This balancing means exposes a minimum surface area of the valve to high pressure forces and isolates the fluid pressure in the pressure lines until interconnection is made by valve actuation.
The valve interconnects the pressure lines by alignment with passages through the valve body. In the neutral position, each pressure line is isolated from the others and independently balanced to prevent the valve body from being jammed against the valve seat or a wall of the valve chamber. In either of the connecting positions, input pressure is supplied to one of the control pressure lines and the other control pressure line is connected to the return line. However, each pair of pressure lines remains isolated from the other pair of pressure lines, and the valve body is independently balanced with respect to pressure forces exerted by each such pair.
The pressure line ports to the valve chamber are coplanar with respect to each other and the passages through the valve body. Valve balancing is achieved in a compact and unexpensive manner through the use of diagonal cross ports drilled through the valve body at each pressure line port. These cross ports permit pressures applied at the pressure line ports to also be applied at other portions of the valve so as to oppose and neutralize the imbalancing forces on the valve body.
Other objects, advantages and novel features of the present invention will become apparent from the following description of the preferred embodiments when taken in conjunction with the accompanying drawings.